1. Field of the Invention
The present invention relates to a method for forming an oblique-etching mask and a method for fabricating a three-dimensional structure with a mask formed according to the formation method. Further, the present invention relates to a method for fabricating a laser device utilizing a three-dimensional photonic crystal.
2. Description of the Related Art
Three-dimensional processing of forming and processing a diagonal hole or a trench pattern in a substrate is a processing method that can improve flexibility of device design and productivity of a three-dimensional structure. In dry-etching such an oblique pattern, if the dry-etching is performed using an etching mask formed approximately perpendicularly to a substrate, an end portion of a mask pattern is shaded by a mask shadowing effect, which makes it difficult to form an oblique pattern shape with high precision. Accordingly, to process the oblique pattern shape with high precision, it is necessary to process the etching mask into such a shape as to reduce the shadowing effect.
Accordingly, Japanese Patent Application Laid-Open No. H05-029283 has proposed an oblique-etching method of forming an oblique trench in a material to be etched by dry etching. In this method, as illustrated in FIGS. 20A to 20C, first, a first etching stopper layer 1117b including a first mask member showing thermal flowability is formed on a material 1111 to be etched, with a portion serving as an opening of a trench sandwiched therebetween. On a layer 1117a including the first mask member, there is formed a second etching stopper layer layered with a layer 1118a including a second mask member having lower thermal flowability than the first mask member, as illustrated in FIG. 20A. Next, by heating the whole, the first etching stopper layer 1117b has flowability to incline a surface thereof, form a taper 1117c as illustrated in FIG. 20B and to perform dry-etching using the taper as a mask as illustrated in FIG. 20C.
On the other hand, conventionally, there has been known a pattern formation technology using ion beam injection as a thin-film processing technology. As such a thin-film processing technology, U.S. Pat. No. 5,236,547 has proposed a method for processing a thin film by the following steps of ion beam injection and applying dry etching to a material to be etched. FIGS. 21A and 21B illustrate a step pattern formation process in thin-film processing disclosed in U.S. Pat. No. 5,236,547 described above. In an ion beam injection process illustrated in FIG. 21A, an injection position of ion beams concentrated on the material to be etched is changed. At the same time, at least one of acceleration voltage, atom type of ion and valence of ion is changed, and ion injection is performed to form an ion concentration peak region in a depth direction of the material to be etched. In FIG. 21A, a region indicated in black is an ion injection region. In a dry etching process illustrated in FIG. 21B, the material to be etched is dry-etched with etching gas for forming ions and an etching inhibition region in an ion concentration peak region of the material to be etched. According to these processes, thin-film processing is implemented. The ion injection region, having higher etching resistance than other regions, is formed with a height difference as illustrated in FIG. 21B. (The reference characters are explained as follows: a film 1212, a substrate 1211, ions 1213 implanted at portions 1212a, an etchant gas 1214 the resulting step-difference pattern 1212b.)
In three-dimensional photonic crystal, as one example of typical structures thereof, there has been known a woodpile structure (or rod-pile structure) disclosed in U.S. Pat. No. 5,335,240. A woodpile structure in the three-dimensional photonic crystal has such a structure as illustrated in FIG. 22. In FIG. 22, a woodpile structure in a three-dimensional structure has a plurality of stripe layers arranged by disposing a plurality of rods 1330 in parallel to each other and periodically in a predetermined in-plane period, which are layered in order as illustrated. Specifically, the three-dimensional structure includes the following four stripe layers: a first stripe layer arranged by disposing a plurality of rods in parallel to each other and periodically in a predetermined in-plane period; a second stripe layer layered on the first stripe layer so as to be orthogonal to the respective rods belonging to the first stripe layer; a third stripe layer layered on the second stripe layer so as to be parallel to the respective rods belonging to the first stripe layer and to be shifted therefrom by one half of an in-plane period; and a fourth stripe layer on the third stripe layer layered so as to be parallel to the respective rods belonging to the second stripe layer and to be shifted therefrom by one half of an in-plane period. The four stripe layers are taken as one set and a plurality of sets thereof are layered in order, so as to form a three-dimensional structure.
In addition, U.S. Patent Publication No. 2005/0207717 has proposed a joint rod type three-dimensional photonic crystalline structure in which a joint larger than an area of an intersection region is disposed at a position corresponding to an intersection of woodpile structure rods in order to provide a complete photonic band gap in a wider wavelength region. Further, Japanese Patent Application Laid-Open No. 2004-219688 has disclosed a thermal adhesion method for different types of members. Next, a process thereof will be described. As illustrated in FIGS. 23A to 23F, a main constitutional layer 1422 of three-dimensional photonic crystal and a light-emitting layer 1424 are tack-welded at 220° C. (FIGS. 23A and 23B). A substrate 1423 on which the light-emitting layer 1424 is placed is thinned by mechanical polishing, as illustrated in FIG. 23C. The main constitutional layer 1422 and the light-emitting layer 1424 are regular-welded at 525° C., as illustrated in FIG. 23D. Then, the substrate 1423 is completely removed by etching process using hydrochloric acid, as illustrated in FIG. 23E. As a result, there is formed three-dimensional photonic crystal in which the light-emitting layer exists on a surface thereof, as illustrated in FIG. 23F.